To heighten image contrast, gradation corrections that calculate the maximum and minimum values of the gradations of each color component of an image signal having a plurality of color components for each pixel in the image, and set the maximum value and the minimum value calculated for each color component to the maximum value and the minimum value of the dynamic range of the gradation scale in the image signal system of the corrected image are carried out (see, for example, patent reference 1 and patent reference 2).